James E. Stowers Jr., Benefactor of Medical Research, Dies at 90

James E. Stowers Jr., the founder of one of the largest investment firms in the United States, who donated a vast portion of his fortune to start a medical research center, died on Monday at his home in Kansas City, Mo. He was 90.

The Stowers Institute for Medical Research announced his death.

Mr. Stowers, known as Jim, founded Twentieth Century Mutual Funds in 1958 with $100,000 he raised from investors. Today the firm, which specializes in mutual funds, manages about $141 billion in assets, according to Gregg Wolper, a senior fund analyst at Morningstar. The company was renamed American Century Investments in 2000.

After Mr. Stowers made a fortune in business, personal health crises prompted him to pour his money into a medical research center. In 1987, he learned he had prostate cancer; six years later, his wife, Virginia, had surgery for breast cancer.

In 1994, they founded the Stowers Institute in Kansas City and created a $2 billion endowment for it with cash gifts and an equity ownership stake of more than 40 percent in American Century. The Stowerses resisted calls to give their money to an established institution, and dismissed concerns that leading scientists would be unwilling to move to Kansas City. The institute opened there in 2000.

A year later, Forbes called Mr. Stowers one of the “world’s biggest givers,” saying he had given about 95 percent of his fortune to endow the institute.

“My wife and I wanted to give back something more valuable than money to the millions of people who made our success possible,” Mr. Stowers said, according to a biography released by American Century, “and we think that through science is the best way we can do it.”

James Evans Stowers Jr. was born Jan. 10, 1924, in Kansas City, to Dr. James Evans Stowers, a surgeon and physician, and Laura Smith Stowers. He was a fighter pilot in the Army Air Corps during World War II and achieved the rank of second lieutenant. He was a captain in the Air Force Reserves until 1957.

His father and his grandfathers were doctors, and after graduating from the University of Missouri he stayed to earn a degree in medicine. But after working at Research Hospital in Kansas City, he decided to pursue a career in business instead.

He joked that his wife, who was a nurse, refused to marry a doctor.

Mr. Stowers is survived by his wife; their three children, Kathleen Stowers-Potter, James Stowers III and Linda Stowers; six grandchildren; and his brother, Richard W. Stowers Sr.

A version of this article appears in print on , on Page A19 of the New York edition with the headline: James E. Stowers Jr., 90; Endowed Research Center. Order Reprints | Today’s Paper | Subscribe